The fundamental objectives of this proposal are two-fold: (1) To continue our structural analysis of the various forms of retrovirus DNA synthesized in vitro; and (2) to delineate the components in addition to the retrovirus reverse transcriptase required to facilitate the synthesis of covalently closed circular forms of viral DNA in vitro. This latter objective is predicated upon major observations from our laboratory concerning retrovirus DNA synthesis in enzymatic reactions in vitro, the most important of which was the demonstration that detergent-disrupted virions of avian retroviruses contain all of the components necessary to facilitate the complete synthesis of mature forms of viral DNA and therefore provide the most useful system available to delineate the components involved in their synthesis. The emphasis of this work is directed at establishing the nature of the components in addition to reverse transcriptase necessary for retrovirus DNA synthesis. Information from these studies should contribute to the elucidation of the mechanism by which RNA tumor formation. To achieve these objectives we propose to employ methodologies already implemented in our laboratory including RNase T1 oligonucleotide mapping, molecular hybridization, electron microscopy, gel electrophoresis, Southern transfer, nucleotide sequencing and a variety of physico-chemical and enzymological methods presently available for the analyses of DNA. Information obtained should contribute to the elucidation of the mechanism by which RNA tumor viruses convert their RNA genome into DNA and thereby replicate and induce cellular transformation.